A team of researchers reporting in the Annals of Allergy, Asthma and Immunology, the journal of the American College of Allergy, Asthma and Immunology (ACAAI), decided to look at whether that rise in food sensitivities could be related to another growing trend during that time period — the use of environmental pesticides and purifying chemicals.

Specifically, the scientists focused on a group of pesticides called dichlorophenols that is also used to purify water. They began with 10,348 participants from the US National Health and Nutrition Examination Survey 2005-2006, 2,548 of whom showed dichlorophenols in their urine. In the end 2,211 were included in the study; food allergy was found in 411 of these participants and 1,016 had an allergy to an environmental agent, whether it was air pollutant or compounds found in products like pesticides. Those with higher levels of dichlorophenols in the body were 80% more likely to have food sensitivity than those with lower levels, and the authors believe the exposure to the chemicals may be contributing to a hyper-sensitive immune system that recognizes even common food proteins as foreign.

“We started to look into the question of why in westernized countries food allergies are so prevalent, says lead study author Dr. Elina Jerschow, an American College of Allergy, Asthma and Immunology (ACAAI) fellow. “Pollutants are so widely available in the West through pesticides, herbicides and insecticides, there may be a link.”

It’s important to understand that the study simply finds an association between pesticide exposure and food allergies; the link does not establish a cause and effect relationship. The authors also say that the study compared rates of food allergies at different times in different populations; a longitudinal study that follows the same group of children over time and monitors their environments and food allergy rates would provide a more definitive answer about the role of pesticides in these allergies.

Yet the correlation raises the possibility that pesticides may be contributing in some way to changing immune sensitivities and influencing the way young children become tolerant to certain antigens in food. In other words, purifying water may strip it of bacteria that may be important in priming our immune systems to recognize and react to more threatening pathogens. Without such “training,” immune systems may mistakenly interpret certain food proteins as harmful, and therefore react to them as if they are a threat.

“In an urbanized setting, we are not exposed to the same bacteria as we used to be,” says Dr. Jerschow. “For example, kids living on farms are exposed to more bacteria and have less allergies. It could be that dichlorophenols prevent us from being exposed to more bugs.”

Dr. Scott Sicherer, professor of pediatrics at the Jaffe Food Allergy Institute at Mount Sinai School of Medicine says the ‘hygiene hypothesis’ is one of many theories that could explain heightened food sensitivies in the U.S. “Nowadays, as the theory goes, we are not living on farms with a large variety of natural germs. We have smaller families, and are otherwise well protected from infections–which is a good thing–so our immune system is not required to fight as many germs,” he says. “This may be leaving the immune system misdirected and ‘looking for a fight’ that leads to an attack on harmless proteins like those in foods, or animal dander or pollens.” In other words, while sanitation practices have protected us from some of the deadly infectious diseases that plagued populations before us, trying to sterilize our environments may not be doing us any favors either. When it comes to keeping our immune systems working properly, it might help to let just a few bugs in.